Genetic Code

Categories: Genetics; reproduction

The genetic code defines each amino acid in a protein, or polypeptide, in terms of a specific sequence of three nucleotides, called codons, in the DNA. The genetic code is therefore the key to converting the information contained in genes into proteins.

The genetic code defines each amino acid in a protein, or polypeptide, in terms of a specific sequence of three nucleotides, called codons, in the deoxyribonucleic acid (DNA). Therefore, the genetic code is called a triplet code. The four different nu-cleotides in DNA can form sixty-four different triplet codons. Because there are only twenty amino acids found in proteins, some amino acids are encoded by more than one codon. Therefore, the genetic code is said to be redundant, or degenerate. Three of the triplet codons do not encode any amino acids. These are stop codons, which identify the end of the message (similar to the period at the end of a sentence) encoded in genes. The genetic code is nearly universal; that is, specific codons code for the same amino acids in nearly all organisms. However, a few exceptions have been found, primarily in mitochondrial DNA (mtDNA), but also in a few protozoa and a single-celled algae, such as Acetabularia. (DNA is found in three places in eu-karyotic cells: the nucleus, plastids, and mitochondria.)

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